Electrode structure for glow discharge tubes



Dec. 19, 1950 H. EPSTEIN ELECTRODE STRUCTURE FOR GLOW DISCHARGE TUBESFiled Aug. 13. 1945 Patented Dec. 19, 1950 "UNITED STATES PATENT ()FFICEELECTRODE STRUCTURE FOR GLOW DISCHARGE TUBES Hirsch Epstein, Chicago,Ill.

Application August 13, 1945, Serial No. 610,578

Claims.

This invention relates to glow discharge tubes, particularly to coldcathode type of glow discharge tubes, and is especially concerned withthe electrode structure for such a tube.

It is one of the objects of the present invention to provide anelectrode structure for a glow discharge tube which electrode structureshall have a large electron emitting surface area in relation to thesize of the electrode.

It is a further object of the present invention to provide an electrodeof the above mentioned character wherein the electron emitting-portionconsists of surfaces opposite one another and comparatively closetogether. This gives a directional effect to the electrodes and servesto control the sputtering that might otherwise take place.

It is a still further object of the present invention'to provide anelectrode wherein the electron emitting portion consists of opposedfaces of concentric cylinders spaced a short distance apart.

It is a still further object of the present invention to provide anelectrode of the above mentioned character wherein the electrodeconstitutes a seal for the end of the glow discharge device.

It is a still further object of the present invention to provide anelectrode which closes the end of the glow discharge device and whichhas a, comparatively large outside exposed surface for facilitating heatradiation.

It is a still further object of the present invention to provide anelectrode of the above mentioned character wherein there is aconsiderable length of electrode material between the portion of theelectrode from which the glow discharge takes place and the portion ofthe electrode that is connected to the glass of the glow discharge tube,thereby providing a temperature gradient such as to prevent excessiveheating of the portion of the electrode that is embedded in the glass ofthe device.

The attainment of the above and further objects of the present inventionwill be apparent from the following specification taken in conjunctionwith the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a diagrammatic view of a glow discharge unit embodyingelectrodes of the present invention;

Figure 2 is an enlarged longitudinal sectional view through one of theelectrodes of the structure of Figure 1;

Figure 3 is an enlarged end view of the electrode of Figure 2;

Figure 4 is a sectional view taken along the line 4-4 of Figure 2;

Figures 5 and 6. are sectional views corresponding to Figure 2 andillustrating modified constructions;

Figure 7 is a sectional view taken along the line 1-! of Figure 6 anddrawn to a smaller scale;

Figure 8 is an end view of a modified form of electrode; and

Figure 9 is a sectional view taken along the line 9-9 of Figure 8.

In Figure 1 there is indicated at I a conventional type of cold cathodeglow discharge tube having similar electrodes 2-2 at opposite endsthereof embodying the present invention. Wires 33 are secured to therespective electrodes for extending the circuit therefrom. Eachelectrode includes a metal closure terminating in a short length ofglass tube 8 which is adapted to be fused tothe main glass tubularportion of the glow discharge device I.

Reference may now be had more particularly to Figures 2, 3 and 4 showingthe construction of an electrode 2 of the glow discharge device 5. Theelectrode comprises a unitary metallic structure including an outertubular body In which extends into and is fused to the end of the shortglass tube 8, the joint between the metal and the glass being made in awell known manner. The outer tubular body H] is open at the end thatfits into the tube 8 and is closed at its opposite end, the closurecomprising a circularly corrugated metal structure which is an integralpart of the outer tubular body Ill. The back of the electrode comprisesa series of annular folds constituting concentric cylinders forming aninside facing outer annular cavity I2 surrounding an outside facingannular cavity I3, which in turn surrounds an inside facing annularcavity it that surrounds an outside facing annular cavity IS. The insidesurface of the annular cavity M is coated with an electron-emittingsubstance which may be of any particular type used in the art, such as,for instance, the alkali-earth metal electronemitters, of which bariumand strontium are examples. The rest of the inside surface of theelectrode body is coated with an insulator it which may comprise aporcelain paste or enamel paint. The insulating paint [6 extends aroundthe curved portions lll8 at the innermost portion of theelectron-emitting cavity M, as indicated at l9, and thus inhibits thesputtering that might otherwise take place. The insulating paint I6 alsoextends around the inner edge of the glass tube 8 at the joint betweenit and the metal electrode, as indicated at l6. This prevents anytendency for arcing to take place at the glass opposite the jointbetween the glass and the metallic structure. The cavities l3 and Iserve for the purpose of increasing the heat radiating surface of theelectrode. The cavity [2 serves to increase thespacing between theelectron-emitting cavity I4 and the place where the electrode is joinedto the glass tube 8. If desired the entire outside surface of theelectrode may be painted with an insulating paint. On the other hand,all or a portion of the outer surface of the electrode may be free ofinsulation to provide for the receiving of a current carrying clip toextend the circuit to the electrode If], in lieu of the use of the wire3 for that purpose.

An electrode of the type illustrated in Figure 2 has a distinctadvantage over those present day electrodes with which the applicant isfamiliar, in that there is provided a very large electronemitting area2U2I on the inside of the annular ring or cavity l4. Also the oppositesurfaces -2l of the electron-emitting surfaces are comparatively closetogether, even as close as two millimeters apart, thus assuring adesirable electrostatic field distribution.

In Figure 5 there is illustrated a modified construction which differsfrom that of Figure 2 essentially in that the fold 12 of Figure 2 hasbeen entirely omitted so that the electron-emitting pocket l4 terminatesat its outer forward peripheral edge in an annular ring which mergeswith the outer tubular body ID. This reduces the distance between theelectron-emitting surface 20 and the tube 8 and is useful in thoseconstructions where the resulting temperature gradient from the tube 8to the electronemitting surface is not excessive.

In Figure 6 I have illustrated an electrode comprising concentriccylinders or rings forming two concentric annular cavities 3il3l, eachclosed at its rear and open at the end facing into the glow dischargetube, said cylinders being joined by an annular disc 32 which may be anintegral part of the folded metal cylinders. The cylindrical side 33 isjoined to a disc 34. The surface of the circular disc 34 which facesinwardly of the tube 41, and the corresponding surface of the annulardisc 32, are painted with a layer 35 of insulating paint, such asporcelain paste paint or enamel, which extends very slightly into thecavities 3!l3|, as indicated at 36. The inner surfaces 33-39 of thecavity 30 and the inner surfaces 48- of the cavity 3| are com-parativelyclose together, say, even as close as two millimeters apart, and thosesurfaces are coated with a substance high in electron-emission, such asone of the alkali-earth electron-emitters. An annular mica discsurrounds the electrode of Figure 6 and maintains it spaced within ashort glass tube 41, which glass tube is adapted to be fused to the endof a long tube to constitute an end of a cold cathode tube. One end ofthe glass tube 41 is open and the opposite end is sealed, as by heatingand pinching the glass together, as indicated at 49. The pinched glassalso seals a conductor 58 which is welded to the disc 34 and extends thecircuit to the electrode.

In Figures 8 and 9 I have shown still another type of electrodeembodying my invention. This electrode embodies two concentric metalliccylinders 6ll6l, welded at one end to a metallic disc 62 and open attheir opposite end. A wire 63 is welded to the disc 62 for extending thecircuit to the disc. The outer surface of the cylinder 60 is coated withan insulating paint 64. The paint 64 extends also over the edges of thecylinders fill-Bl which are opposite the disc 62 and, optionally, theinsulating paint may extend a very short distance inside the cylinder 60and a very short distance over the outer peripheral wall of the cylinder6|. This would be for the purpose of controlling the electron emissionnear the edge of the electrode and prevent sputtering of the electrode.The cylinders 60-6! may be of only slightly different diameters so thatthe annular space 66 between the cylinders may be even as small as a fewmillimeters. The outside surface of the cylinder 6| and the insidesurface of the cylinder 60 are coated with a substance high inelectron-emitting qualities, of the type hereinabove referred to, sothat the electrons are emitted from the electrode at the oppositesurfaces forming the annular space 66.

The electrode of Figures 8 and 9 may be mounted in a short glass tube inthe same manner as illustrated for the electrode of Figure 6, whichshort tube may then be fused to the end of a long tube, as is known inthe art.

It is to be noted that the electrodes in each of the embodiments hereinillustrated have electron-emitting surfaces comprising concentriccylinders. This provides a very large electronemitting surface areawithin a compact space, with resulting advantages. Furthermore, theelectron-emitting surfaces of the concentric cylinders are opposite oneanother and comparatively close together. This controls the field ofdistribution of the electron flow.

In compliance with the requirements of the patent statutes I have hereshown and described a few preferred embodiments of my invention. It is,however, to be understood that the invention is not limited to theprecise constructions here shown, the same being merely illustrative ofthe principles of the invention. What I consider new and desire tosecure by Letters Patent is:

1. An electrode comprising a tube and a closure for one end thereofcomprising a central portion and surrounding said central portion acircular fold forming an annular cylindrical pocket the inside of whichis open at the front, the inner surface of said annular pocket thatfaces inwardly of the tube being coated with an electron-emittingmaterial.

2. An electrode comprising a tube and a closure for one end thereofcomprising a central portion and surrounding said central portion acircular fold forming an annular pocket open at the front, the surfaceof said annular pocket which is exposed at the open front of theelectrode being coated with an electron-emitting material and theportion of the electrode surface adjacent the annular pocket at the openend thereof being covered with an insulating covering.

3. An electrode for an electric discharge device. comprising a tube, aclosure sealing the end of the tube, said closure being sealed to andextending across one end of the tube, said closure comprises acontinuous imperforate metal sheet having a plurality of concentriccylindrical surfaces coated with electron-emitting material.

4. An electrode for an electric discharge device, comprising a tube, aclosure sealing the end of the tube, said closure being sealed to andextending across one end of the tube, said closure having a centralportion and surrounding said central portion said closure having acircular fold forming an annular pocket opening into the tube the innersurface of the pocket being coated with electron-emitting material.

5. An electrode for a cold cathode discharge unit, said electrodecomprising a metallic end closure for the unit, said closure having aplurality of concentric corrugations, facing surfaces of thecorrugations on the interior side of the end closure being coated withelectron emitting material and constituting the electron-emitting partof the electrode.

6. A glow discharge device comprising a tube having an ionizable gaseousatmosphere therein, means sealing the opposite ends of the tube, saidmeans comprising metallic electrodes and a sealing joint between eachelectrode and the tube, each electrode comprising a continuousimperferate sheet having at least one set of concentric cylindricalelectron-emitting surfaces with the space between the surfacescommunicating with the interior of the device.

7. An electrode comprising a tube open at one end and sealed at theopposite end by an imperiorate metal member extending across the end ofthe tube and sealed around its periphery to the end of the tube, themetal member having a plurality of concentric convolutions so that onesurface of each convolution is open to the interior of the tube and theopposite surface is open to the atmosphere that surrounds the tube, andmeans on portions of the surface of the metal member facing inwardly ofthe tube for controlling the emission of electrons.

8. An electrode comprising a tube open at one end and sealed at theopposite end by an imperforate metal member extending across the end ofthe tube and sealed at its periphery to the end of the tube toconstitute a seal for said opposite end of the tube, the metal memberhaving a plurality of concentric convolutions so that one surface ofeach convolution is open to the interior of the tube and the oppositesurface is open to the atmosphere that surrounds the tube, certainconvolutions having a layer of electron-emitting material on a portionof the surface thereof that is open to the interior of the tube.

9. An electrode comprising a tube open at one end and sealed at theopposite end by an imperforate metal member extending across the end ofthe tube and sealed at its periphery to the end of the tube, the metalmember having a plurality of concentric convolutions so that one surfaceof each convolution. is open to the interior of the tube and theopposite surface is open to the atmosphere that surrounds the tube,certain convolutions having a layer of electron-emitting material on aportion of the surface thereof that is open to the interior of the tubeand on the same surface thereof having a covering of insulationextending from the electron-emitting layer to the tube.

10. An electrode comprising a tube, a metal member at the end of thetube, the metal member having a plurality of convolutions about an axisparallel to the longitudinal axis of the tube, certain convolutionshaving a layer of electronemitting material on a. portion of the surfacethereof that is open to the interior of the tube, and a covering ofinsulation on the member beween concentric convolutions, said insulationterminating at the layer of electron-emitting material.

HIRSCI-I EPSTEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 745,367 Moore Dec. 1, 19031,046,004 Moore Dec. 3, 1912 1,667,977 Lucian May 1, 1928 1,827,292Laube Oct. 13, 1931 1,891,475 Hotchner Dec. 20, 1932 2,016,437 Jones,Oct. 8, 1935 2,020,727 Gaides et a1 Nov. 12, 1935 2,029,986 Claude Feb.4, 1936 2,267,318 Aicher Dec. 23, 1941 2,281,878 Heger May 5, 19422,330,032 Dailey Sept. 21, 1943 2,345,794 Chevigny Apr. 4, 1944 FOREIGNPATENTS Number Country Date 399,317 Great Britain Oct. 5, 1933 444,545Great Britain Mar. 23, 1936

